Witch of the Wishing Well
Talk about it here.
She would come up from a well where a rupture in time was actually located. Anyone who came into contact with her would have parts of their psyche stolen and start exhibiting symptoms similar to obsessive compulsive disorder.
The Tenth Doctor, Gabby Gonzalez and Cindy Wu arrived in Drewbury and soon learned of the legend of the witch. After a close encounter with the witch, the Doctor realised she was a composite entity, made up of seven different psyches who had merged. They lured the witch back to the cave where the time fissure was located and the Doctor built a device that allowed her to communicate with him.
The Doctor discovered that the "witch" was in fact the remains of seven Gallifreyan children from the Dark Times of Gallifrey. They had been taken to the Untempered Schism, a gap in fabric of time and space through which one could see all of the Time Vortex. Though this was usually an initiation ceremony for Time Lords, the children had been thrown into the Schism. One of them was a time sensitive who tried to save the others by forming a composite being, resulting in the creation of the witch. They were stealing parts of other people's psyches to try to replace the parts they had lost.
Though they begged the Doctor to help them, they were quickly pulled back to Ancient Gallifrey, forever lost in the Time Vortex. This restored the psyches of their victims, but the events left the Doctor greatly disturbed. (COMIC: The Wishing Well Witch)